Apparatus for cutting bone

ABSTRACT

An apparatus ( 10 ) for cutting bone includes a shaft member ( 12 ) having a central axis ( 14 ) and extending between a proximal end portion ( 16 ) and a distal end portion ( 18 ). The proximal end portion ( 16 ) has a first surface ( 32 ) adapted to receive repetitive impacts. The distal end portion ( 18 ) includes a cutting blade ( 40 ) extending in a first plane between a shield section ( 46 ) and a guide portion ( 60 ). The shield section ( 46 ) and the guide section ( 60 ) project axially beyond the cutting blade ( 40 ) to recess the cutting blade ( 40 ) in the distal end portion ( 18 ). The shield section ( 46 ) includes an inwardly facing shield surface ( 48 ) which extends in a second plane that is transverse to the first plane of the cutting blade ( 40 ). The apparatus ( 10 ) is a form of an osteotome that is particularly useful for certain spine-related surgical procedures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent application Ser. No. 10/540,381, filed Jun. 23, 2005, which is a National Stage Application of International Application No. PCT/US2003/041 043, filed on Dec. 23, 2003, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/436,867, filed Dec. 27, 2002. The subiect matter of the aforementioned applications is incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an apparatus for cutting bone and, in particular, is directed to a uniquely designed osteotome that is useful in cutting vertebrae.

BACKGROUND OF THE INVENTION

A known procedure for treating vertebral compression fractures and other bone-related disorders is vertebral augmentation with bone cement. Vertebral augmentation can be performed by the direct-injection of liquid cement into the collapsed vertebral body (commonly known as “vertebroplasty”). Vertebral augmentation can also be performed after the restoration of the vertebrae to near normal vertebral body anatomy and creation of an internal cavity with the use of an inflatable bone tamp. This minimally invasive procedure is commonly known as “kyphoplasty” (see, for example, U.S. Pat. Nos. 4,969,888 and 5,108,404). During the kyphoplasty procedure, the inflatable bone tamp is inserted through a small skin incision which accommodates a working tube passed into the vertebral body. Inflation of the bone tamp compresses the cancellous bone and desirably moves the fractured cortical bone to its pre-fractured orientation, creating a cavity within the vertebral body that can then be filled with a settable material such as a cement or any number of synthetic bone substitutes. In effect, the procedure sets the vertebral body at or near its pre-fracture position and creates an internal cast, protecting the vertebral body from further fracture and/or collapse.

As compared to a traditional vertebroplasty procedure, kyphoplasty restores the vertebrae to a pre-fractured condition and the injected bone filler is less likely to leak out of the vertebral body during a kyphoplasty procedure. However, under some circumstances, it has been observed that unpredictable reductions can occur with the kyphoplasty technique in chronic or partially healed collapsed vertebral bodies. Under those circumstances, the surgeon would typically resort to a large, open operation to re-align any post-traumatic kyphosis. Further, inadequate reductions can occur with certain other spinal deformities such as scoliosis and kyphosis using the known techniques and surgical tools. The large, open operations can carry with them significant morbidity in an already physiologically compromised elderly population. The principle benefit of a percutaneous minimally invasive approach, which is the hallmark of the kyphoplasty procedure, is the minimal morbidity associated with the procedure. In this light, additional tools are required to further the kyphoplasty technique, achieve better anatomic re-alignment of the spine, and maintain the minimally invasive nature of the surgery. The additional tools will be deployed through small working portals and be able to achieve the desired strategic vertebral osteotomies to move bone in three dimensional space. One such desirable tool would provide a minimally invasive means to safely cut the lateral (or side) wall of a vertebral body, such as a lateral wall with a prior, and at least partially healed, compression fracture.

SUMMARY OF THE INVENTION

The present invention is an apparatus for cutting bone. The apparatus comprises a shaft member having a central axis and extending between a proximal end portion and a distal end portion. The proximal end portion has a first surface adapted to receive repetitive impacts. The distal end portion includes a cutting blade extending in a first plane between a shield section and a guide section. The shield section and the guide section project axially beyond the cutting blade to recess the cutting blade in the distal end portion. The shield section includes an inwardly facing shield surface which extends in a second plane that is transverse to the first plane of the cutting blade.

The present invention further provides an apparatus for cutting through the cortical bone of a vertebral body, the cortical bone having an outer peripheral surface and an inner surface surrounding cancellous bone. The apparatus comprises an elongate member having a shaft portion extending along a central axis between a proximal end portion and a distal end portion. The proximal end portion has a platform adapted to receive repetitive impacts to advance the elongate member along the vertebral body. The distal end portion of the elongate member includes an arcuate cutting blade extending in a first plane between first and second tip portions. The cutting blade is adapted to cut through the cortical bone of the vertebral body as the elongate member is advanced. The first tip portion has a shield surface which extends in a second plane that is transverse to the first plane of the cutting blade. The shield surface shields the cutting blade to prevent undesired cutting of soft tissues present on the outer peripheral surface of the vertebral body. The second tip portion comprises a blunt tooth extending generally parallel to the central axis and acting as a guide to ensure that the distal end portion of the elongate member follows the contours of the inner surface of the vertebral body as the elongate member is advanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:

FIG. 1 is a side view of an apparatus for cutting bone constructed in accordance with the present invention;

FIG. 2 is a plan view taken along line 2-2 in FIG. 1;

FIG. 3 is a plan view illustrating the apparatus of FIG. 1 being used to cut a lateral wall of a vertebral body; and

FIG. 4 is a side view taken along line 4-4 in FIG. 3, with soft tissues on the outside of the vertebral body omitted for clarity.

DESCRIPTION OF EMBODIMENTS

The present invention relates to an apparatus for cutting bone and, in particular, is directed to a uniquely designed osteotome that is useful in cutting vertebrae. As representative of the present invention, FIGS. 1 and 2 illustrate an apparatus 10 comprising an elongate member 11 made of a medical grade metal such as stainless steel. The elongate member 11 includes a shaft portion 12 extending along a central axis 14 between a proximal end portion 16 and a distal end portion 18 of the apparatus 10. In accordance with one embodiment of the invention, the shaft portion 12 and the distal end portion 18 are designed to fit through a 5 mm (inner diameter) cannula 20 (FIG. 3) and thus have a maximum outer diameter of 4.8 mm. It should, however, be understood that the apparatus 10 and the cannula 20 could have correspondingly larger or smaller diameters.

The proximal end portion 16 of the apparatus 10 has a platform 30 with a planar surface 32 adapted to receive repetitive impacts from another tool, such as a hammer (not shown), to advance the elongate member 11. The platform 30 has a larger outer diameter than the shaft and distal end portions 12 and 18 of the apparatus 10 to facilitate receiving impacts with a hammer.

The distal end portion 18 of the apparatus 10 includes an arcuate cutting blade 40 (FIG. 2) extending in a first plane between first and second tip portions 42 and 44. The cutting blade 40 is recessed axially from the terminal ends of the tip portions 42 and 44 and is adapted to cut through cortical bone as the elongate member 11 is advanced. The first tip portion 42 comprises a shield section 46 having a shield surface 48 (FIG. 1). The shield surface 48 extends in a second plane that is transverse to the first plane of the cutting blade 40. In the embodiment of FIGS. 1 and 2, the shield surface 48 is perpendicular to the cutting blade 40. As may be seen in FIG. 1, the shield section 46 at the distal end portion 18 is approximately the same width (or diameter) as the shaft portion 12 of the apparatus 10. The shield section 46 further includes an arcuate end surface 50 and an outwardly facing ramp surface 52 (FIG. 2). It is contemplated that the end surface 50 could also be sharp similar to a periosteal elevator.

The second tip portion 44 comprises a guide section 60 that extends generally parallel to the central axis 14. The guide section 60 includes a blunt tooth 62 with a bulbous terminal end 64. As may be seen in FIG. 1, the guide section 60 is substantially narrower in width (or diameter) than the shield section 46 and projects axially beyond the end surface 50 of the shield section.

FIGS. 3 and 4 illustrate use of the apparatus 10 to cut bone. Specifically, FIGS. 3 and 4 illustrate the apparatus 10 cutting through cortical bone 70 of a vertebral body 72. The cortical bone 70 of the vertebral body 72 has an outer peripheral surface 74 and an inner surface 76 that surrounds cancellous bone 78. As best seen in FIG. 4, the vertebral body 72 has a partially healed compression fracture to be treated via a kyphoplasty procedure. In order to perform the kyphoplasty procedure, the partially healed cortical bone 70 in the lateral wall 80 of the vertebral body 72 must be cut to release the upper and lower end plates 82 and 84 of the vertebral body so that an inflatable bone tamp (not shown) inserted inside the vertebral body can, when inflated, move the upper and lower end plates back to their pre-fractured positions (illustrated in dashed lines in FIG. 4).

Access to the lateral wall 80 of the vertebral body 72 occurs in a minimally invasive manner via the cannula 20. After drilling a passage through a transverse process 86 of the vertebral body 72, the cannula 20 is placed through the transverse process. The distal end portion 18 of the apparatus 10 is then inserted through the cannula 20 and into engagement with the lateral wall 80 of the vertebral body. Next, the blunt tooth 64 of the guide section 60 is tapped through the cortical bone 70 of the vertebral body 72 so that the cutting blade 40 is positioned to cut the cortical bone as shown in FIG. 3.

From the position of FIG. 3, the distal end portion 18 of the apparatus 10 is advanced along the lateral wall 80 of the vertebral body 72 through impact blows, either by hand, hammer, or other suitable means to the platform 30 at the proximal end portion 16. As the distal end portion 18 advanced, the cutting blade cuts the lateral wall 80 in order to release the end plates 82 and 84 of the vertebral body 72. Significantly, the bulbous terminal end 64 of the guide section 60 follows the contours of the inner surface 76 of the cortical bone 70 and prevents the distal end portion 18 from straying out of engagement with the vertebral body 72 as the distal end portion is advanced.

Furthermore, as the distal end portion 18 of the apparatus 10 is advanced, the shield surface 48 acts as a shield for the cutting blade 40 to prevent undesired cutting of soft tissues 90, such as blood vessels, nerves, and muscles, present on the outer peripheral surface 74 of the vertebral body 72. In addition, as the distal end portion 18 is advanced, the arcuate end surface 50 of the shield section 46 slides underneath the soft tissues 90 on the outer peripheral surface 74 of the vertebral body 72 and cooperates with the ramp surface 52 to lift the soft tissues off of the outer peripheral surface. This geometry at the distal end portion 18 allows the apparatus 10 to safely cut the lateral wall 80 so that a kyphoplasty procedure can be used to treat the compression fracture of the vertebral body 72 in a minimally invasive fashion.

From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, it should be understood that, depending on the nature of the condition of a given vertebral body, the lateral wall on the opposite side of the vertebral body 72 shown in FIG. 3, or on both sides of the vertebral body, may need to be cut in order to release the end plates of the vertebrae. In such situations, the apparatus 10 would be used in an identical fashion with access through a cannula placed through the other transverse process. Further, it should be understood that the apparatus 10 disclosed herein could be used to cut through other areas of cortical bone in vertebrae, as well as cortical bone in other bones in a mammalian body. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. 

1. A method for cutting bone, the bone having an outer peripheral surface and an inner cortical surface, said method comprising the steps of: providing an apparatus comprising a shaft member having a central axis and extending between a proximal end portion and a distal end portion, the distal end portion including a cutting blade extending in a first plane between a shield section and a guide section that extends axially beyond said shield section, the guide section including a bulbous terminal end, the shield section and the guide section projecting axially beyond the cutting blade to recess the cutting blade in the distal end portion, the shield section including an inwardly facing shield surface which extends in a second plane that is transverse to the first plane of the cutting blade; positioning the apparatus so that the distal end portion of the apparatus engages the outer peripheral surface of the bone; and repetitively impacting the proximal end portion of the apparatus so that the cutting blade cuts the bone.
 2. The method of claim 1 wherein said step of repetitively impacting the proximal end portion of the apparatus further comprises the step of sliding an arcuate end surface of the shield section underneath soft tissues present on the outer peripheral surface of the bone as the shaft member is advanced, the shield surface functioning as a shield for the cutting blade to prevent undesired cutting of the soft tissues.
 3. The method of claim 2 wherein said step of repetitively impacting the proximal end portion of the apparatus further comprises the step of using the shield section, which includes an outwardly facing ramp surface for cooperating with the arcuate end surface, to lift the soft tissues off of the outer peripheral surface of the bone as the shaft member is advanced.
 4. The method of claim 1 wherein said step of providing an apparatus with a guide section including a bulbous terminal end comprises the step of providing a guide section including a bulbous terminal end that is substantially sphere shaped.
 5. A method for cutting bone, the bone having an outer peripheral surface and an inner cortical surface, said method comprising the steps of: providing an apparatus comprising a shaft member having a central axis and extending between a proximal end portion and a distal end portion, the distal end portion including a cutting blade extending in a first plane between a shield section and a guide section that extends axially beyond said shield section, the guide section including a bulbous terminal end, the shield section and the guide section projecting axially beyond the cutting blade to recess the cutting blade in the distal end portion, the shield section including an inwardly facing shield surface which extends in a second plane that is transverse to the first plane of the cutting blade; positioning the apparatus so that the distal end portion of the apparatus engages the outer peripheral surface of the bone; and repetitively impacting the proximal end portion of the apparatus so that the cutting blade cuts the bone; wherein said step of positioning the apparatus so that the distal end portion of the apparatus engages the outer peripheral surface of the bone further comprises the steps of: providing a cannula to facilitate delivery of the apparatus; inserting the apparatus into the cannula; and tapping the proximal end portion of the apparatus so that the blunt tooth of the guide section penetrates the outer peripheral surface of the bone, the guide section comprising a blunt tooth extending generally parallel to the central axis and acting as a guide to ensure that the distal end portion of the shaft member follows the contours of the inner cortical surface of the bone as the shaft member is advanced.
 6. A method for cutting through the cortical bone of a vertebral body having upper and lower end plates, the cortical bone having an outer peripheral surface and an inner surface surrounding cancellous bone, said method comprising the steps of: providing an apparatus comprising an elongate member having a shaft portion extending along a central axis between a proximal end portion and a distal end portion, the distal end portion of the elongate member including an arcuate cutting blade extending in a first plane between first and second tip portions, the first and second tip portions extending axially beyond the cutting blade to recess the cutting blade, the first tip portion having a shield surface which extends in a second plane that is transverse to the first plane of the cutting blade, the second tip portion extending axially beyond said first tip portion and comprising a blunt tooth extending generally parallel to the central axis and a bulbous terminal end; forming a passage through a transverse process of the vertebral body to access a lateral wall of the vertebral body; inserting the apparatus into the passage so that the distal end portion engages the lateral wall of the vertebral body; and impacting the proximal end portion of the apparatus so that the distal end portion is advanced along the lateral wall of the vertebral body and the cutting blade cuts the lateral wall to release the end plates of the vertebral body.
 7. The method of claim 6 wherein said step of repetitively impacting the proximal end portion of the apparatus further comprises the step of sliding an arcuate end surface of the shield section underneath soft tissues present on the outer peripheral surface of the bone as the shaft member is advanced, the shield surface functioning as a shield for the cutting blade to prevent undesired cutting of the soft tissues.
 8. The method of claim 7 wherein said step of repetitively impacting the proximal end portion of the apparatus further comprises the step of using the shield section, which includes an outwardly facing ramp surface for cooperating with the arcuate end surface, to lift the soft tissues off of the outer peripheral surface of the bone as the shaft member is advanced.
 9. The method of claim 6 wherein said step of inserting the apparatus into the passage further comprises the steps of: inserting a cannula into the passage; and tapping the proximal end portion of the apparatus so that the blunt tooth of the guide section penetrates the outer peripheral surface of the cortical bone, the second tip portion including a bulbous terminal end that helps the second tip portion follow the contours of the inner surface of the vertebral body as the elongate member is advanced.
 10. The method of claim 6 further comprising the step of cutting the cortical bone to release the upper and lower plates of the vertebral body and inserting an inflatable bone tamp inside the vertebral body so that the upper and lower end plates move back to their pre-fractured positions when the inflatable bone tamp is inflated. 